1. Technical Field of the Invention
The present invention relates to a cosmetic treatment regime or regimen process especially for depigmenting and/or bleaching the skin, by application thereon of at least one compound of dithiolane type.
2. Description of Background and/or Related and/or Prior Art
The color of human skin depends on many factors and especially on the seasons of the year, race and sex; it is mainly determined by the nature and concentration of melanin produced by the melanocytes. Melanocytes are specialized cells that synthesize melanin, by means of particular organelles, the melanosomes. At different periods in their life, certain individuals develop darker and/or more colored marks on their skin and especially on the hands, giving the skin a heterogeneous appearance. These marks are also due to a large concentration of melanin in the keratinocytes located at the surface of the skin.
The administration of highly effective, harmless topical depigmenting substances is most particularly sought to treat regional hyperpigmentations caused by melanocyte hyperactivity, such as idiopathic melasmas, occurring during pregnancy (“pregnancy mask” or chloasma) or oestro-progestative contraception, localized hyperpigmentations caused by benign melanocytic proliferation and hyperactivity, such as senile pigmentation marks known as actinic lentigo, accidental hyperpigmentations, possibly due to post-lesional cicatrization or photosensitization, and also certain leukodermias, such as vitiligo. For the latter (cicatrizations that may result in a scar, giving the skin a whiter appearance), failing the possibility of repigmenting the damaged skin, depigmentation of the areas of residual normal skin is completed to impart to the skin as a whole a uniform white complexion.
The mechanism of formation of skin pigmentation, i.e., the formation of melanin, is particularly complex and schematically involves the following main steps:                Tyrosine->Dopa->Dopaquinone->Dopachrome->Melanin        
Tyrosinase (monophenol dihydroxyl phenylalanine: oxygen oxidoreductase EC 1.14.18.1) is the essential enzyme participating in this sequence of reactions. It especially catalyzes the reaction for the conversion of tyrosine into dopa (dihydroxyphenylalanine) by virtue of its hydroxylase activity, and the reaction for the conversion of dopa into dopaquinone by virtue of its oxidase activity. This tyrosinase acts only when it is in the mature form, under the influence of certain biological factors.
A substance is recognized as being depigmenting if it acts directly on the vitality of the epidermal melanocytes in which melanogenesis takes place and/or if it interferes with one of the steps in the biosynthesis of melanin either by inhibiting one of the enzymes involved in melanogenesis or by inserting itself as a structural analogue of one of the chemical compounds of the melanin synthesis chain, which chain may then become blocked and thus ensure depigmentation.
The substances most commonly employed as depigmenting agents are, more particularly, hydroquinone and its derivatives, in particular its ethers such as hydroquinone monomethyl ether and monoethyl ether. Although they have a certain level of efficacy, these compounds are, unfortunately, not free of side effects on account of their toxicity, which may make them difficult or even hazardous to use. This toxicity arises from the fact that they participate in fundamental mechanisms of melanogenesis by killing cells which then run the risk of disturbing their biological environment and which consequently oblige the skin to eliminate them by producing toxins.
Thus, hydroquinone is a compound that is particularly irritant and cytotoxic to melanocytes, and whose total or partial replacement has been envisaged by many researchers.
Substances are thus sought, which do not participate in the melanogenesis mechanism, but which act upstream of tyrosinase by preventing its activation, and which are consequently much less toxic. Kojic acid, which complexes the copper present in the active site of tyrosinase, is commonly used as a tyrosinase activation inhibitor. Unfortunately, this compound is unstable in solution, which somewhat complicates the formulation of the composition.
Need continues to exist for a novel human skin-bleaching agent whose action is just as efficient as the known agents, but which does not have their drawbacks, i.e., which is non-irritant, non-toxic and/or non-allergenic to the skin, while at the same time being stable in a composition, or, alternatively, which has reinforced action so as to be able to be administered in smaller amount, which considerably reduces the observed side effects.